Many semiconductor devices use metal-silicon compounds called silicides to enhance conductivity between source and drain features and conductive lines. Salicides are self-aligned silicides. Self-aligned refers to a manufacturing technique where a gate electrode region of a transistor is used as a mask for doping the source and drain. Some techniques for forming salicides over source and drain features include depositing a metal layer over a surface of a semiconductor assembly including the source and drain features. The assembly is then annealed to form a salicide in a reaction between silicon atoms in the source and drain features and metal atoms in the metal layer. The unreacted metal is then removed using an etching process.
The reaction to form salicide consumes silicon atoms in the source and drain features. If the source and drain features have an insufficient amount of silicon at a surface interface with the metal layer, in some instances, the salicide is also etched through during the etching process to remove unreacted metal. Etching through the salicide creates openings that can form short circuits when metal contacts are deposited on the source and drain features. Additionally, in situations where silicon atoms are unevenly concentrated in the source and drain features, voids can form in the salicide and cause the semiconductor device to malfunction.